The present invention relates to a method and/or system for the alkylation of an olefin with an isoparaffin utilizing a catalyst mixture comprising a volatility reducing additive, hydrogen fluoride and water. More specifically, the invention relates to a method and/or system for removing water from the catalyst mixture to avoid water buildup therein.
The use of catalytic alkylation processes to produce branched hydrocarbons having properties that are suitable for use as gasoline blending components is well known in the art. Generally, the alkylation of olefins by saturated hydrocarbons, such as isoparaffins, is accomplished by contacting the reactants with an acid catalyst to form a reaction mixture, settling the reaction mixture to separate the catalyst from the hydrocarbons, thereby forming a catalyst mixture phase and an alkylation reactor effluent, and further separating the alkylation reactor effluent, for example, by fractionation, to recover the separate product streams. Normally, the alkylation reactor effluent of the alkylation process contains hydrocarbons having five to ten carbon atoms per molecule. In order to have the highest quality gasoline blending stock, it is preferred for the alkylate hydrocarbons formed in the alkylation process to be highly branched and contain seven to nine carbon atoms per molecule.
Recent efforts to improve conventional hydrogen fluoride catalyzed alkylation processes have resulted in the development of new catalyst compositions that contain hydrogen fluoride and a volatility reducing additive. These new catalyst compositions have been found to be quite effective as an alkylation catalyst and to provide many other favorable benefits.
In such processes which include a volatility reducing additive in the catalyst, the regeneration of the catalyst mixture typically includes stripping a slip stream of the circulating catalyst mixture with an isoparaffin producing an overhead stream containing isoparaffin, hydrofluoric acid and water (preferably substantially absent of water) and a bottoms stream containing hydrofluoric acid (preferably in very small quantities), volatility reducing additive, and an acid soluble oil (ASO) produced as a by-product in the alkylation reaction. Because of the azeotrope formed between HF and water, it is often not possible to provide dry HF as the overhead stream. Thus, as described in U.S. Pat. No. 5,759,937 issued to Keith W. Hovis and Richard L. Anderson, a stripper side-draw stream is often required to remove water from the system by removing the HF/water azeotrope material from the sidedraw and allowing substantially water free HF to pass overhead. However, during certain upset conditions wherein excess water enters the system, either with the makeup HF or from feed contaminant upsets which can generate water, the sidedraw stream often cannot remove enough of the excess water. Excess water in the catalyst mixture can result in lower alkylation quality and can have other non-beneficial effects on the alkylation process, including corrosion problems. Therefore, development of an efficient process and/or system for removing water from a circulating alkylation catalyst mixture would be a significant contribution to the art.
It is, thus, an object of the present invention to provide an improved process for removing water from an alkylation catalyst mixture.
A further object of the present invention is to provide an improved system to be used in removing water from an alkylation catalyst mixture which is economical in construction and reliable and efficient in operation.
A yet further object of the present invention is to provide a method and/or system for preventing the accumulation of water in the catalyst mixture of an alkylation process.
Still another object of the present invention is to provide a method and/or system for preventing the accumulation of water in the catalyst mixture of an alkylation process while minimizing the loss of HF with the water removed from the system.
A yet further object of the present invention is to provide an improved system to be used in preventing the accumulation of water in the catalyst mixture of an alkylation process which includes means for controlling the concentration of water in the catalyst mixture.
According to a first embodiment of the present invention, an alkylation process is provided and comprises the steps of:
a) contacting a hydrocarbon mixture comprising at least one olefin and at least one isoparaffin with a catalyst mixture comprising HF, a volatility reducing additive and water within a reaction zone to thereby produce a reaction zone effluent;
b) passing the reaction zone effluent to a settler wherein the reaction zone effluent is separated into a hydrocarbon phase and a catalyst mixture phase comprising HF, water and volatility reducing additive;
c) removing at least a portion of the hydrocarbon phase from the settler to form a settler effluent stream;
d) passing the settler effluent stream to a first separator;
e) removing an overhead stream from the first separator;
f) condensing at least a portion of the overhead stream to form an HF/water stream comprising HF, water and volatility reducing additive; and
g) passing the HF/water stream to a second separator for separation into a modified HF stream comprising HF and volatility reducing additive and into an HF/water azeotrope stream comprising HF and water.
According to a second embodiment of the present invention, an alkylation process is provided and comprises the steps of:
a) contacting a hydrocarbon mixture comprising at least one olefin and at least one isoparaffin with a catalyst mixture comprising HF, a volatility reducing additive and water within a reaction zone to thereby produce a reaction zone effluent;
b) passing the reaction zone effluent to a settler wherein the reaction zone effluent is separated into a hydrocarbon phase and a catalyst mixture phase comprising HF, water, volatility reducing additive and acid soluble oil;
c) removing at least a portion of the hydrocarbon phase from the settler to form a settler effluent stream;
d) passing the settler effluent stream to a first separator;
e) removing a first separator overhead stream from the first separator;
f) condensing at least a portion of the first separator overhead stream to form an HF/water stream comprising HF, water and volatility reducing additive;
g) passing the HF/water stream to a second separator for separation into a modified HF stream comprising HF and volatility reducing additive and into an HF/water azeotrope stream comprising HF and water; and
h) passing at least a portion of the catalyst mixture phase to a third separator for separation into a third separator overhead stream comprising HF and water and into a third separator bottoms stream comprising HF, water, ASO and volatility reducing additive.
According to a third embodiment of the present invention, an alkylation process is provided and comprises the steps of:
a) contacting a hydrocarbon mixture comprising at least one olefin and at least one isoparaffin with a catalyst mixture comprising HF, a volatility reducing additive and water within a reaction zone to thereby produce a reaction zone effluent;
b) passing the reaction zone effluent to a settler wherein the reaction zone effluent is separated into a hydrocarbon phase and a catalyst mixture phase comprising HF, water, volatility reducing additive and acid soluble oil;
c) removing at least a portion of the hydrocarbon phase from the settler to form a settler effluent stream;
d) passing the settler effluent stream to a first separator;
e) passing at least a portion of the catalyst mixture phase to a second separator for separation into a second separator overhead stream comprising HF and water and separation into a second separator bottoms stream comprising HF, water, ASO and volatility reducing additive;
f) blocking the passing of the at least a portion of the catalyst mixture phase to the second separator in step e;
g) removing a first separator overhead stream from the first separator;
h) condensing at least a portion of the first separator overhead stream to form an HF/water stream comprising HF, water and volatility reducing additive; and
i) passing the HF/water stream to the second separator for separation into a modified HF stream comprising HF and volatility reducing additive and into an HF/water azeotrope stream comprising HF and water.
According to a fourth embodiment of the present invention, an alkylation system is provided and comprises:
an alkylation reactor;
a settler, having an upper portion, an intermediate portion and a lower portion;
a first separator, having an upper portion, an intermediate portion and a lower portion;
a second separator, having an upper portion, an intermediate portion and a lower portion;
a third separator, having an upper portion, an intermediate portion and a lower portion;
a condenser unit;
first conduit means operably related to the alkylation reactor for introducing a hydrocarbon feedstock comprising olefins and isoparaffins into the alkylation reactor;
second conduit means operably related to the alkylation reactor for introducing a catalyst mixture comprising a volatility reducing additive, hydrofluoric acid and water into the alkylation reactor;
third conduit means operably related to the alkylation reactor and operably related to the settler for withdrawing a reaction zone effluent from the alkylation reactor and for introducing the reaction zone effluent into the intermediate portion of the settler, the upper portion of the settler being operable for containing a hydrocarbon phase separated from the reaction zone effluent and the lower portion of the settler being operable for containing a catalyst mixture phase separated from the reaction zone effluent;
fourth conduit means operably related to the settler and operably related to the first separator for withdrawing at least a portion of the hydrocarbon phase from the upper portion of the settler and for introducing the at least a portion of the hydrocarbon phase into the intermediate portion of the first separator;
fifth conduit means operably related to the first separator and operably related to the condenser unit for withdrawing an overhead stream from the upper portion of the first separator and for introducing the overhead stream into the condenser unit;
sixth conduit means operably related to the condenser unit and operably related to the second separator for withdrawing an HF/water stream from the condenser unit and for introducing the HF/water stream into the intermediate portion of the second separator;
seventh conduit means operably related to the sixth conduit means and operably related to the settler for withdrawing a portion of the HF/water stream from the sixth conduit means and for introducing the portion of the HF/water stream into the intermediate portion of the settler;
eighth conduit means operably related to the first separator for withdrawing an alkylate product stream from the first separator;
ninth conduit means operably related to the settler and operably related to the alkylation reactor for withdrawing at least a portion of the catalyst mixture phase from the settler and for introducing the at least a portion of the catalyst mixture phase into the alkylation reactor;
tenth conduit means operably related to the settler and operably related to the second separator for withdrawing a catalyst mixture phase regeneration stream from the lower portion of the settler and for introducing the catalyst mixture phase regeneration stream into the intermediate portion of the second separator;
eleventh conduit means operably related to the second separator and operably related to the settler for withdrawing a second separator overhead stream from the upper portion of the second separator and for introducing the second separator overhead stream to the intermediate portion of the settler;
twelfth conduit means operably related to the second separator and operably related to the third separator for withdrawing a second separator bottoms stream from the lower portion of the second separator and for introducing the second separator bottoms stream to the intermediate portion of the third separator, the upper portion of the third separator being operable for containing ASO and the lower portion of the third separator being operable for containing HF and volatility reducing additive;
thirteenth conduit means operably related to the twelfth conduit means for withdrawing a purge stream from the twelfth conduit means; and
fourteenth conduit means operably related to the third separator and operably related to the settler for withdrawing a third separator bottoms stream from the lower portion of the third separator and for introducing at least a portion of the third separator bottoms stream into the intermediate portion of the settler.
The alkylation system can further comprise control means operably related to the sixth conduit means, the seventh conduit means, the ninth conduit means, the tenth conduit means, the twelfth conduit means, and the thirteenth conduit means for controlling the water concentration in the catalyst mixture phase regeneration stream to a level equal to a set point water wt. %, based on the total weight of the catalyst mixture phase.
Other objects and advantages will become apparent from the detailed description and the appended claims.